Organic dust toxic syndrome (ODTS) is an acute, febrile, noninfectious, flu-like, short-term reaction that can be seen in a range of situations after inhalation of substances that give rise to an inflammatory reaction in the lungs. There are anecdotical reports suggesting that ODTS is a risk factor for asthma in farmers. In a cross-sectional study, questionnaires were mailed to farmers in middle Sweden and southern Sweden. Sixty percent of the farmers (1004 men and 129 women) responded to the questionnaire. The mean age was 51 years. Nine percent were smokers and 24 percent ex-smokers. The female farmers had a significantly higher prevalence of doctor-diagnosed asthma compared to the males, 8.3 percent compared to 4.5 percent (p<0.05) and worked significantly more often in all productions involving animals. Regression analysis of male farmers showed that ODTS was a risk factor for respiratory symptoms such as wheeze, work related wheeze, nightly breathlessness and chronic bronchitis. Long time in agricultural work was another risk factor for wheeze, work related wheeze, doctor-diagnosed asthma and chronic bronchitis. Swine farming was a risk factor for chronic bronchitis. Possible mechanism behind these findings and prevention strategies will be discussed.